- if the damage die (six-sided) is a 6, the helm comes into play- the helm is dashed from the owner's head but the damage die is thrown again (if it's still a six, too bad)- the helm might be destroyed in the process; throw 12+ (on d20) for the helm to survive intact

I've used this a LOT in my games and the players love it. My only suggestion is that you don't incorporate this rule with "shattering shields" as it makes fighters near-indestructible; which might be perfect if you want that style of game.

This looks like a neat house rule addition. I just hopped over to the DD forums to take a look, I see he has both shield and helm rules in play. Agree, that definitely makes fighting-men far more heroic then they already are, essentially getting two free get-out-of-death cards. And there are always spare shields or helms available after most humanoid combats, so there is no reason the fighting-man can't restock.